Economical and efficient methods and apparatus for purifying contaminated water, particularly water containing fatty acids, have long been sought. Contaminated water, e.g., waters containing soluble nitrogen compounds, suspended organic colloidal emulsions or suspensions such as effluents from meat processing plants, dairies, cheese processing plants, bakeries, chemical plants, paper plants and petroleum plants and effluents including raw sewage are of particular interest.
The colloids have a negative charge which prevents them from coalescing and makes filtration or separation practically impossible. Previous methods for water purification include combining the fatty acid contaminated water with metallic ions released from electrodes during electrolysis to form hydrophobic, metallic soaps. Bivalent or trivalent metal ions are released from electrodes during electrolysis and combine with the fatty acids to form an insoluble flocculent. The flocculant, in turn, entrains or absorbs other impurities present in the contaminated water. Thus, the flocculant serves as a transport medium to remove not only fatty acids, but also other impurities from the water. In order to ensure continuous production of ions, the electrodes were disposed in a moving bed of solid particles. The solid particles were kept in motion by the flow of process water through the electrolysis chamber in order to continuously abrade and clean the electrode surfaces. The flocculant and entrained impurities were directed to a flocculation/separation basin where the flocculent and entrained impurities were separated by flotation, leaving purified water for withdrawal from the basin.
Electrolytic water treating systems, including electro-flotation and electrocoagulation systems, while functional, have difficulties when their electrodes become covered with an insoluble layer that is not removable by merely changing the polarity of the electrodes. This is especially true when sewage water containing fatty acids is electrolyzed with metal electrodes which form an insoluble metal soap at the surface of the anode which is difficult to remove.
Current electrolytic water treating systems clean the electrodes by a moving bed of hard particles and introduces air before the electrolytic cell to move the bed and the water through the system. However, it has been found that bubbles before the electrolytic cells increase the electrical resistance between the electrodes thereby requiring higher voltages and inducing excess wear on electrodes, walls and parts of the cell.
After the majority of contaminants have been removed, remaining dissolved and suspended contaminating materials need to be removed and have been electrolytically treated with chlorine. Chlorine is normally made electrolytically, continuously introducing a concentrated salt solution (chloride ions) into the anode compartment of an electrolysis cell which is separated from the cathode compartment by a permeable diaphragm. Before the advent of ion exchange diaphragms the diaphragm were made of many plies of asbestos paper between anode and cathode to prevent as much as possible mixing of the caustic produced in the cathode compartment with the chlorine produced in the anode compartment. Currently, cationic ion exchange diaphragms that prevent the flow of anions and of solutions from one compartment to another are typically used.
Chlorine as sodium hypochlorite may be made by electrolyzing salt water without the use of diaphragms. This process is especially useful for swimming pool applications. This process has the disadvantage of using salt and the calcium and magnesium present in the water to form carbonates which deposit on the cathode eventually isolating it and preventing current flow between the electrodes. The cathode must then be cleaned with acid to remove the calcareous coating.
The standard electrolytical technique to chlorinate water in swimming-pools is to provide a separate cell containing a high concentration of common salt which upon electrolysis gives sodium hypochlorite or chlorine which is fed into the swimming-pool. Theoretically, it is possible to add sufficient common salt to the swimming-pool water and to electrolyze it directly. However, this technique has the disadvantage that the water tastes salty to the bathers and that the calcium contained in the water deposits onto the cathodes to such an extent that the flow of the current stops or is impaired. Changing of polarity to remove the calcium deposits on the cathodes has been found in practice to lead to corrosion of the cathode.
The water purification industry has continued to seek new and improved methods for removing fatty acids and other contaminants from water. Accordingly, there has been a long-felt but unfulfilled need for more economical, more efficient and more convenient methods for purifying water, particularly water contaminated with fatty acids and other contaminants and treating the purified for eventual discharge or use.